xmonad/XMonad.hs

{-# OPTIONS -fglasgow-exts #-}
-----------------------------------------------------------------------------
-- |
-- Module      :  XMonad.hs
-- Copyright   :  (c) Spencer Janssen 2007
-- License     :  BSD3-style (see LICENSE)
--
-- Maintainer  :  sjanssen@cse.unl.edu
-- Stability   :  unstable
-- Portability :  not portable, uses cunning newtype deriving
--
-----------------------------------------------------------------------------
--
-- The X monad, a state monad transformer over IO, for the window
-- manager state, and support routines.
--

module XMonad (
    X, WindowSet, WorkspaceId(..), ScreenId(..), XState(..), XConf(..), Layout(..),
    Typeable, Message, SomeMessage(..), fromMessage,
    runX, io, withDisplay, withWorkspace, isRoot, spawn, restart, trace, whenJust, whenX
  ) where

import StackSet (StackSet)

import Control.Monad.State
import Control.Monad.Reader
import System.IO
import System.Posix.Process (executeFile, forkProcess, getProcessStatus, createSession)
import System.Exit
import System.Environment
import Graphics.X11.Xlib
import Data.Typeable

import qualified Data.Map as M

-- | XState, the window manager state.
-- Just the display, width, height and a window list
data XState = XState
    { windowset         :: !WindowSet           -- ^ workspace list
    , xineScreens       :: ![Rectangle]         -- ^ dimensions of each screen
    , dimensions        :: !(Position,Position) -- ^ dimensions of the screen,
    , statusGap         :: !Int                 -- ^ width of status bar
                                                -- used for hiding windows
    , layouts           :: !(M.Map WorkspaceId (Layout, [Layout]))  }
                       -- ^ mapping of workspaces to descriptions of their layouts

data XConf = XConf
    { display           :: Display      -- ^ the X11 display

    , theRoot           :: !Window      -- ^ the root window
    , wmdelete          :: !Atom        -- ^ window deletion atom
    , wmprotocols       :: !Atom        -- ^ wm protocols atom

    , normalBorder      :: !Color       -- ^ border color of unfocused windows
    , focusedBorder     :: !Color     } -- ^ border color of the focused window

type WindowSet = StackSet WorkspaceId Window ScreenId

-- | Virtual workspace indicies
newtype WorkspaceId = W Int deriving (Eq,Ord,Show,Read,Enum,Num,Integral,Real)

-- | Physical screen indicies
newtype ScreenId    = S Int deriving (Eq,Ord,Show,Read,Enum,Num,Integral,Real)

------------------------------------------------------------------------

-- | The X monad, a StateT transformer over IO encapsulating the window
-- manager state
--
-- Dynamic components may be retrieved with 'get', static components
-- with 'ask'. With newtype deriving we get readers and state monads
-- instantiated on XConf and XState automatically.
--
newtype X a = X (ReaderT XConf (StateT XState IO) a)
    deriving (Functor, Monad, MonadIO, MonadState XState, MonadReader XConf)

-- | Run the X monad, given a chunk of X monad code, and an initial state
-- Return the result, and final state
runX :: XConf -> XState -> X a -> IO ()
runX c st (X a) = runStateT (runReaderT a c) st >> return ()

-- ---------------------------------------------------------------------
-- Convenient wrappers to state

-- | Run a monad action with the current display settings
withDisplay :: (Display -> X a) -> X a
withDisplay f = asks display >>= f

-- | Run a monadic action with the current workspace
withWorkspace :: (WindowSet -> X a) -> X a
withWorkspace f = gets windowset >>= f

-- | True if the given window is the root window
isRoot :: Window -> X Bool
isRoot w = liftM (w==) (asks theRoot)

------------------------------------------------------------------------
-- Layout handling

-- | The different layout modes
-- 'doLayout', a pure function to layout a Window set 'modifyLayout', 
-- 'modifyLayout' can be considered a branch of an exception handler.
--
data Layout = Layout { doLayout     :: Rectangle -> [Window] -> X [(Window, Rectangle)]
                     , modifyLayout :: SomeMessage -> Maybe Layout }

-- Based on ideas in /An Extensible Dynamically-Typed Hierarchy of Exceptions/,
-- Simon Marlow, 2006. Use extensible messages to the modifyLayout handler.
-- 
-- User-extensible messages must be a member of this class:
--
class Typeable a => Message a

--
-- A wrapped value of some type in the Message class.
--
data SomeMessage = forall a. Message a => SomeMessage a

--
-- And now, unwrap a given, unknown Message type, performing a (dynamic)
-- type check on the result.
--
fromMessage :: Message m => SomeMessage -> Maybe m
fromMessage (SomeMessage m) = cast m

-- ---------------------------------------------------------------------
-- General utilities

-- | Lift an IO action into the X monad
io :: IO a -> X a
io = liftIO

-- | spawn. Launch an external application
spawn :: String -> X ()
spawn x = io $ do
    pid <- forkProcess $ do
        forkProcess (createSession >> executeFile "/bin/sh" False ["-c", x] Nothing)
        exitWith ExitSuccess
    getProcessStatus True False pid
    return ()

-- | Restart xmonad via exec().
--
-- If the first parameter is 'Just name', restart will attempt to execute the
-- program corresponding to 'name'.  Otherwise, xmonad will attempt to execute
-- the name of the current program.
--
-- When the second parameter is 'True', xmonad will attempt to resume with the
-- current window state.
restart :: Maybe String -> Bool -> X ()
restart mprog resume = do
    prog <- maybe (io $ getProgName) return mprog
    args <- if resume then gets (("--resume":) . return . show . windowset) else return []
    io $ catch (executeFile prog True args Nothing)
               (const $ return ()) -- ignore executable not found exception

-- | Run a side effecting action with the current workspace. Like 'when' but
whenJust :: Maybe a -> (a -> X ()) -> X ()
whenJust mg f = maybe (return ()) f mg

-- | Conditionally run an action, using a X event to decide
whenX :: X Bool -> X () -> X ()
whenX a f = a >>= \b -> when b f

-- | Grab the X server (lock it) from the X monad
-- withServerX :: X () -> X ()
-- withServerX f = withDisplay $ \dpy -> do
--     io $ grabServer dpy
--     f
--     io $ ungrabServer dpy

-- | A 'trace' for the X monad. Logs a string to stderr. The result may
-- be found in your .xsession-errors file
trace :: String -> X ()
trace msg = io $! do hPutStrLn stderr msg; hFlush stderr